Anesthesiology

Patient Positioning During Anesthesia: Lithotomy

Patient transfer

Prior to achieving any surgical position, the patient must be transferred onto the operating room table. The final position of the patient is of the utmost importance, but achieving these positions requires careful planning and coordination by the operating room team. The overall plan for each patient transfer should be discussed prior to any movement.

Frequently, the patient can assist in positioning prior to induction of anesthesia. However, under general anesthesia, the operating room team must carefully move and position each patient. Pertinent patient comorbidities should be reviewed. For example, patients with morbid obesity or unstable spine fractures will require additional staff for transfer and positioning. When the patient is moved after the induction of general anesthesia, the anesthesiologist must be aware of any blood pressure alterations and ensure a safe systemic blood pressure prior to any patient movement.

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All monitors, intravenous lines, and the endotracheal tube need to be carefully managed when moving a patient. The eyes should be taped to avoid corneal abrasion. With excellent communication, patients can be safely and successfully transferred within the operating room.

Lithotomy

The lithotomy position is a variation of the supine position in which the hips are flexed, the legs abducted, and knees flexed. The legs are secured in leg supports such as the candy cane, knee crutch, or boot support. As with the supine position, the arms can either be tucked at the patient’s side or abducted to less than 90 degrees and supinated on padded arm boards. The foot section of the operating room table is then lowered to allow surgical access to the perineum.

What common procedures are performed in this position?

The lithotomy position is used regularly in gynecologic, urologic, and colorectal procedures.

What are the common variations of this position?

In the lithotomy position, the legs can be positioned into a low, standard, or high position as dictated by the surgical team. As with the supine position, the patient in the lithotomy position can be positioned into the Trendelenburg or reverse Trendelenburg position.

What are the physiologic changes when placing a patient in this position?

The lithotomy position is similar to the supine position, but with the addition of bilateral elevation of the legs. This will create similar physiologic changes as seen during the supine position. However, the anesthesiologist can expect a further decrease in FRC and lung compliance compared to the supine position due to additional abdominal compression with an elevated leg position.

The effects of closing capacity and intrapulmonary shunt are similar to the supine position. Cardiovascular effects of lithotomy positioning are also similar to those in the supine position. However, with leg elevation, there is a transient rise in cardiac output secondary to an increased return of in venous blood from the legs augmenting preload.

What are the options for anesthetic management?

Nearly all types of anesthesia can be provided with the patient in the lithotomy position. These include general anesthesia with endotracheal intubation or LMA, neuraxial, and MAC.

Patient body habitus and exact leg height must be determined prior to the procedure when contemplating MAC or the use of LMA. The physiologic changes as well as the comfort of the patient might make these techniques unsuitable or unsafe.

What complications are associated with this position?

Peripheral nerve injury has been reported after surgery in the lithotomy position. Injury to the common peroneal nerve appears to be the most common nerve injured.

Symptoms include motor weakness in ankle extension, ankle eversion, and foot dorsiflexion. This can be accompanied by variable sensory loss of the dorsal foot and lateral leg. The mechanism of injury appears to be related to stretch and compression of the peroneal nerve.

Overall, the risk of peroneal nerve injury increases with the length of surgery. Reports indicate a 100-fold increase in injury risk per hour spent in the lithotomy position. This can be minimized by intraoperative position changes of the legs to limit the time spent in lithotomy. Recent evidence suggests a decreasing incidence of common peroneal nerve injury due to better awareness and proper surgical positioning.

Other potential nerve injuries include compression of the lateral femoral cutaneous nerve leading to lateral thigh pain or meralgia paresthetica. The femoral nerve can be injured via compression beneath the inguinal ligament with extreme thigh abduction and external rotation of the hip.

Compartment syndrome is another potential serious complication related to the lithotomy position. The exact mechanism is not completely understood. Overall, arterial pressure of the lower extremity decreases proportionately with the height of leg raise in the lithotomy position. Also, lower extremity compartment pressures increase predictability for unknown reasons when placed in the lithotomy position. The combination of a lower arterial pressure and elevated compartment pressure potentially lead to ischemia of the lower extremity musculature and soft tissue.

Of all standard surgical positions, lithotomy, followed by the lateral decubitus position, puts the patient at the greatest risk for compartment syndrome. Length of time spent in the lithotomy position is the only established evidence-based risk factor and 2 hours appears to be the point at which this risk substantially increases.

Other potential risk factors include obesity, blood loss, vascular disease, and intraoperative hypotension. Intermittent pneumatic compression devices used to increase lower extremity circulation have not been implicated in the development of compartment syndrome in the lithotomy position.

What strategies can be used to decrease the risk of injury in this position?

As with the supine position, the patient’s arm must be properly positioned to decrease the risk of peripheral nerve injury. A more detailed discussion of arm position can be found in the chapter on the supine position.

The lithotomy position does increase the risk of crush injury to the patient’s hands and fingers. If the arms are tucked at the patient’s side, the hands might rest at the break in the operating room table. When the foot section of the operating room table is brought back to the normal position at the conclusion of the procedure, the table can impinge the hand or fingers leading to serious crush injury. Careful attention must be paid to the hands prior to raising the foot of the table.

As previously stated, the lithotomy position is associated with several lower extremity nerve injuries, including the common peroneal, lateral femoral cutaneous, femoral, and sciatic nerves.

In the lithotomy position, the legs are positioned into maneuverable supports, allowing the surgeon the freedom to move either leg in nearly all planes of motion.

Specific care must be paid to the position of the knee. Proper positioning does not allow external compression or fixation of the lateral leg at the fibular head to avoid pressure on the peroneal nerve.

The risk of nerve injury increases with every hour spent in the lithotomy position. Intraoperative position changes of the legs can minimize the time spent in lithotomy and potentially limit nerve injuries.

To limit the risk of injury to the lateral femoral cutaneous, femoral, and sciatic nerves, excess hip flexion and abduction should be avoided.

Another complication of the lithotomy position is lower extremity compartment syndrome. Although the exact mechanism of injury is not completely understood, the current literature emphasizes an increased risk during prolonged periods of time spent in the lithotomy position. At 2 hours with the legs raised, the incidence of compartment syndrome increases. In surgeries lasting longer than 2 hours, intermittent repositioning or lowering of the legs is recommended and may decrease the overall incidence of compartment syndrome.